Method of preparing phosphine



METHOD OF PREPARING PHOSPHINE Filed July 27, 1960 1 Z i 2| POLAR Z ,SOLVENT 7,

Z -H |z 4 T f Y J QM, A 3 ym .3 34W 91 36 United States Patent Ofi 3 ,109,790 Patented Nov. 5, 1963 ice 3,109,790 METHUD F PREPARENG PHOSPHENE George T. Miller, Lewiston, N.Y., assignor to Hooker Chemical Corporation, Niagara Falls, N.Y., a corporation of New York Filed July 27, 1960, Ser. No. 45,655 23 Claims. (Cl. 204-101) 'lhis invention relates to the preparation of phosphine from molten yellow phosphorus by electrolysis.

Heretofore, phosphine has been prepared by the reaction of metallic phosphides or phosphonium halides with water, and by the hydrolysis of elemental phosphorus. These methods have been unsatisfactory because of the high production costs and/ or because the phosphine prodnot is in an impure form.

United States Patent No. 1,375,819, issued April 26, 1921, to Henry Blumenberg, Jr., discloses a method for preparing arsine by the electrolysis of a salt or oxide of arsenic in the presence of sulfuric acid and potassium sulfate or other compounds capable of liberating nascent hydrogen upon electrolysis. However, phosphine is not produced under the conditions set forth by Blumenberg when an oxide or salt of phosphorus is employed.

W. R. Grove, in the Journal of the Chemical Society, Vol. 16 (1863), pp. 263272, discloses the use of an electric current to boil moist molten phosphorus and produces phosphine thereby. Such a technique requires a high voltage, and converts only a small amount of phosphorus to phosphine.

It is an object of this invention to provide a method of producing phosphine by electrolytic means.

Another object of the invention is to provide a more economical method of producing phosphine.

Still another object of the invention is to provide a method of producing phosphine in a form substantially free from phosphorus hydrides and other phosphorus impurities.

A further object of this invention is to provide a novel method of dispersing elemental phosphorus in the catholyte of an electrolytic cell for the production of phosphine.

These and other objects of the invention will be apparent from the following detailed description of the invention.

It has now been discovered that phosphine can be prepared in an electrolytic cell having a cathode, a catholyte, an anolyte, and an anode, by dispersing elemental phosphorus in a polar solvent, employing this phosphorus-containing solvent as a catholyte, and passing an electric current between the cathode and anode through the catholyte and anolyte, and recovering the phosphine-containing gas produced at the cathode.

The accompanying drawing is a schematic illustration of a suitable electrolytic cell for carrying out the novel process.

Referring to the drawing, there is shown a cell vessel having a cathode section 11, and an anode section 12, the sections 11 and 12 being separated by a porous diaphragm 13. The gas tight cover 14, having ports 15, 16, 17, 18, 19 and 20, is secured .to the top of cell vessel 10. Catholyte 21 is added to catholyte section 11 by means of funnel 22, which extends through port 15, up to catholyte level 23. The catholyte 21 is comprised of elemental phosphorus dissolved in a polar solvent which is discussed more fully hereinafter. Cathode 24 extends through port 16 into catholyte 21. Cathode 24 is illustrated as a solid plate, but other forms of cathodes can be employed, and will be discussed more fully hereinafter.

Anolyte 25 is fed into anode section 12 through funnel 26, which extends through port 17, up to level 27. Anolyte 25 is an aqueous electrolyte as discussed more fully hereinafter. Anode 28 extends through port 18; into anolyte 25, contained in anode section 12. Electric conductors 22 and 30 connect the anode 28 and the cathode 24, respectively, to the positive and negative poles, respectively, of a source of electrical energy 31.

When an electric current is impressed upon the system a phosphine-containing gas is generated in the cathode section 11, and is discharged through catholyte gas discharge line 32, which extends through port. 19. At the same time the anolyte gas formed in the anode section 12, is discharged through anolyte gas discharge line 33, which extends through port 20.

Cathode section port 34 is provided for removing catholyte from the cathode section 11, and anode section port 35 is provided for removing anolyte from the anode section 12.

If desired, a motor driven impeller 36, or other suitable agitation means, may be positioned in the bottom portion of cathode section 11 to efiect agitation of the phosphoruscontaining catholyte.

It will be recognized by those skilled in the art that the design of the electric cell shown in the drawing may be modified without departing from the spirit of the invention. For example, the cathode is shown in the drawing as a solid plate, but a liquid cathode such as mercury may be employed if desired. In such a case liquid mercury is placed in the bottom of the cathode section 11 and an electric conductor 30 is extended through port 16 into the liquid cathode at the bottom of cathode section 11.

Cell vessel 10 may be constructed of any impervious material of suitable corrosion resistance such as glass, ceramics, rubber lined steel and the like.

Porous diaphragm 13 may be constructed of any suitable porous material such as sintered glass, porous Alundurn, ion-exchange membranes, plastic cloth, glass cloth and the like.

Any material having a hydrogen overvoltage as normally measured in the absence of phosphorus exceeding the hydrogen overvoltage of smooth platinum may be employed as the cathode. Typical cathodic materials include lead, lead-mercury amalgam, tin, mercury, cadmium, copper, bismuth, aluminum, zinc, brass, silver, nickel, tellurium, gold, and alloys thereof. For example, various tin-bismuth alloys, bismuth-lead alloys, lead-tin alloys, nickel alloys with such metals as iron, copper, chromium, and the like may be employed. Black phosphorus may also be employed as a cathode material.

It is desirable to employ a cathode in a form having a high unit of area per unit of weight. As indicated previously, the drawing shows the cathode in the form of a solid plate. If desired, when a solid cathode is employed, the cathode may have the form of a helical coil, wire gauze or screen, perforated sheets, porous sponge metal, metal wool, and the like.

Suitable anode materials include lead, lead-antimony, lead dioxide, platinum, graphite and stainless steel.

In order to enhance the yield of phosphine, it is necessary to obtain maximum dispersion of elemental phosphorus in the catholyte. This dispersion can be effected by one of two novel embodiments of the invention. In the first embodiment the catholyte is prepared by dissolving elemental phosphorus in a polar solvent capable of dissolving elemental phosphorus under the electrolysis conditions obtained. Suitable polar solvents include alcohols such as methanol, ethanol, butanol, allyl alcohol, benzyl alcohol, glycol, and the like, water, a mixture of carbon disulfide and Water, carbon disulfide-phosphorus and mixtures thereof. In addition, satisfactory results may also be obtained with solvents such as acetic acid, dioxane, phenol and the like. When phosphorus is dissolved in carbon disulfide there is the apparent formation of a Zwitter-ion compound P +--C(=S)S, which appears to act as a polar solvent for the purposes of this invention. In preparing the catholyte in accordance with the second novel embodiment, a solution of elemental phosphorus in a solvent for phosphorus which is miscible with an aqueous electrolyte, is then admixed with an aqueous electrolyte, whereby a major portion of the phosphorus dissolved in the solvent forms a colloidal precipitate. Suitable solvents include the aforesaid polar solvents as well as anhydrous ammonia, ethyl ether and the like.

Any aqueous electrolyte which is non-reactive with molten phosphorus and through which hydrogen ions may be transported under the electrolysis conditions employed, may be employed as the catholyte. For example, suitable aqueous solutions for dispersing the phosphorus solution include water, phosphoric acid, hydrochloric acid, and the like.

The amount of phosphorus dissolved in the solvent will depend upon the solubility characteristics of the solvent,

. but preferably a concentration of phosphorus in the solvent of between about 0.0001 percent by weight up to the saturation concentration is employed.

When an aqueous electrolyte is admixed with the solvent containing dissolved phosphorus to produce colloidal phosphorus, the weight ratio of aqueous electrolyte to phosphorus-containing solvent may be between 0.01:1 and about 90:1 and is preferably between about 0.1 :1 and about 5:1. 7

Either basic or acidic aqueous electrolyte solutions may be employed as the anolyte. Typical examples of suitable compounds, in aqueous solution, which may be employed as the anolyte include phosphoric acid, sulfuric acid, hy drochloric acid, sodium chloride, lithium chloride, potassium chloride, sodium sulfate, potassium sulfate, monosodium phosphate, disodium phosphate, acetic acid, am monium hydroxide, and mixtures thereof.

Molten white phosphorus, sometimes referred to as yellow phosphorus, is preferably employed as the source of phosphorus for the production of phosphine, but other alloropic forms of phosphorus may be employed if desire The temperature of the catholyte during electrolysis may be maintained between about zero and about one hundred degrees centigrade. Temperature control of the catholyte may be readily obtained by means of a constant temperature bath (not shown in the drawing), surrounding cell vessel 10, but any suitable temperature control means may be employed. For example, on start-up of the electrolytic process the catholyte may be heated to a temperature within the aforesaid temperature range by means of an external source of heat, and maintained at this temperature by means of a constant temperature bath.

During electrolysis the catholyte gas produced in accordance with the instant novel technique is a mixture of phosphine and hydrogen containing the compound employed as a' solvent for phosphorus. The catholyte. gas, after removal from the cell, is cooled to a temperature sufficient to condense the gaseous solvent compound. The resulting condensate is recycled for dissolving additional phosphorus for use as a catholyte in the cell. The

phosphine-hydrogen-containing gas recovered from the condensation step contains as high as ninety percent phosphine or higher. An important advantage of this process is that the phosphine-containing gas is relatively free from other phosphorus hydrides, as compared to phosphine produced by prior art techniques, and as a result, the gas is not spontaneously flammable when contacted with air.

The phosphine-hydrogen-containing gas may be treated by conventional methods to separate hydrogen, or may be used as is in the preparation of organic phosphorus compounds such as tetrakis (hydroxymethyl) phosphonium chloride.

The composition of the anolyte gas will depend upon the composition of the electrolyte. For example, when Ygen containing acids, bases or salts are used as the anolyte, the anolyte gas predominates in oxygen. However, when hydrochloric acid or halide salts are employed as the anolyte, the anolyte gas predominates in chlorine or the corresponding halogen.

The rate of production of phosphine and the purity of the phosphine product depend upon the current and current density employed during electrolysis. It will be recognized by those skilled in the art that the optimum current and current density will depend upon the cell design employed. However, any conditions of operation that yield phosphine at a rate and of the purity consistent with economic operations may be employed. For ex- 7 ample, a cathodic current density between about one and about twenty-five amperes persquare foot, and a voltage drop across the system between five and about fifty volts will normally yield phosphine at a rate and of a purity which is economically feasible.

Spent catholyte may be continuously or intermittently removed from the cell and either discarded and replaced with fresh catholyte or else employed to dissolve additional phosphorus and then returned to the cathode section. The anolyte may be replenished by a similar technique.

The following examples are presented to define the invention more fully without any intention of being limited thereby. All parts and percentages are by weight unless otherwise specified.

Example 1 An electrolytic cell was constructed from two methyl methacrylate blocks having a two inch diameter by one inch recess in one face of each block. A cation exchange membrane, positioned between the two blocks divided the cell into cathode and anode compartments. A porous lead plate was inserted in the cathode compartment to serve as the cathode, and a porous lead dioxide plate was inserted in the anode compartment to serve as the anode. The cathode and anode were connected to a source of direct current. A port at the top of the cathode section and a port at the top of the anode section permitted discharge of the catholyte and anolyte gases.

Yellow phosphorus was dissolved in ethyl alcohol in proportions sufficient to yield a saturated solution at sixtyfive degrees centigrade, and thirty-two cc. of the resulting solution was added to the cathode section of the cell to serve as the catholyte. Thirty-two cc. of forty percent aqueous phosphoric acid was added to the anode section to serve as the anolyte. An electric current was passed through the cell system, the current varying between 0.2 ampere and one ampere, the voltage therein being thirteen volts and 46.5 volts. The temperature of the catholyte was maintained at sixty-five degrees centigrade. The catholyte gas was collected and passed through NaOBr solution. The phosphine concentration in the catholyte gas was found tobe 42.5 percent by volume.

Example 2 Using the cell of Example 1, a catholyte was prepared by dissolving white phosphorus in ethanol, in proportions to yield a saturated solution at sixty-five degrees centigrade. Twenty cc. of this solution was admixed with twelve cc. of forty percent aqueous phosphoric acid solution and then added to the cathode section of the cell. The cell was operated for a period of about thirty-five minutes at a current of one ampere and a voltage which varied between about five and 5.9 volts. The temperature of the catholyte was about sixty-five degrees centigrade.

During this period one hundred and twelve cc. of catholyte gas was formed, which was analyzed by absorp tion in an aqueous NaOBr solution. The phosphine concentration of the catholyte gas was 14.1 percent by volume.

Example 3 I An electrolytic cell was constructed as follows: The cathode compartment was comprised of a six inch by three-quarter inch O.D porous Alundum tube diaphragm having a glass tube communicating with the top portion thereof, adapted to discharge cathode gas and through which a platinum wire electrode was inserted to be concentric in the Alundum tube. A glass C-tube was connected to the bottom portion of the Alundum tube and to the glass tube above the top of the Alundum tube. This cathode compartment was inserted into a one liter vessel to function as the anode compartment, having a platinum wire anode parallel to the porous Alundum diaphragm. The cathode and anode compartments were filled with an aqeuous forty percent phosphoric acid solution, which was maintained at seventy-five degrees centigrade. Sufficient molten phosphorus was added to the cathode compartment to just seal the lower horizontal leg of the G-tube. The upper level of the molten phosphorus was about one inch below the lower tip of the platinum Wire cathode. A direct current of six amperes at a voltage of 4.4 volts was impressed upon the cell. The cathode gas which bubbled from the cathode caused a gas-lift effect upon the catholyte, thereby circulating the catholyte up through the porous Alundum tube, downward through the C-tube, across the pool of molten phosphorus and up through the Alundum tube, in a cyclic manner. Circulation of the catholyte in this manner caused the continuous transfer of phosphorus from the lower leg of the C-tube to the area adjacent to the cathode. Cathode gas containing phosphine was discharged from the top of the cathode compartment and collected. The phosphine concentration averaged about forty percent by volume. Interruption of circulation, due to evaporation of catholyte during overnight operation, caused the concentration of phosphine to decrease to about eight percent. However, when the catholyte level was re-established and circulation resumed, the phosphine concentration rapidly increased to about forty percent by volume.

It will be recognized by those skilled in the art that various modifications of the invention are possible, some of which have been referred to above. Therefore, I do not wish to be limited except as defined by the appended claims:

I claim:

1. The process for the production of phosphine in an electrolytic cell comprised of a cathode, a catholyte, an anolyte, and an anode, which comprises dissolving elemental phosphorus in a polar solvent, contacting the resulting solution as said catholyte with said cathode, and passing an electric current between said cathode and said anode through said catholyte and said anolyte, whereby a phosphine-containing gas is produced at the cathode.

2. The process of claim 1 wherein said polar solvent is selected from the group consisting of methanol, ethanol, butanol, allyl alcohol, benzyl alcohol, glycol, water, carbon disulfide-phosphorus and mixtures thereof.

3. The process of claim 1 wherein said polar solvent is ethanol.

4. The process of claim 1 wherein said polar solvent is water.

5. The process of claim 1 wherein said polar solvent is a mixture of water and carbon disulfide.

6. The process of claim 1 wherein said polar solvent is carbon disulfide-phosphorus.

7. The process of claim 1 wherein the concentration of said elemental phosphorus to said polar solvent is between about 0.001 percent and about the saturation concentration.

8. The process of claim 1 wherein said catholyte is maintained free from contact with said anode.

9. The process of claim 1 wherein a phosphine-containing gas produced at the cathode is subjected to fractional condensation to condense said polar solvent, and the resulting polar solvent condensate is recycled to dissolve additional elemental phosphorus.

10. The process of claim 1 wherein at least a portion of the catholyte is withdrawn from the cell vessel, additional phosphorus is dissolved in said portion of catholyte, and the resulting solution is recycled to the cell vessel.

11. The process for the production of phosphine in an electrolytic cell comprised of a lead cathode, a catholyte, an aqueous phosphoric acid anolyte, and a lead oxide anode, which comprises dissolving elemental phosphorus in ethanol, contacting the resulting solution as said catholyte with said cathode, and passing an electric current between said cathode and said anode through said catholyte and said anolyte, whereby a phosphine-containing gas is produced at the cathode.

12. The process for the production of phosphine in an electrolytic cell comprised of a cathode, a catholyte, an anolyte, and an anode, which comprises dissolving elemental phosphorus in a solvent, admixing the resulting solution with an aqueous electrolyte, whereby a colloidal dispersion of elemental phosphorus is obtained, contacting the resulting colloid-containing solution as said catholyte with said cathode, and passing an electric current between said cathode and said anode through said catholyte and said anolyte, whereby a phosphine-containing gas is produced at the cathode.

13. The process of claim 12 wherein said aqueous electrolyte is sulfuric acid.

14. The process of claim 12 wherein said aqueous electrolyte is acetic acid.

15. The process of claim 12 wherein said aqueous electrolyte is an aqueous phosphoric acid solution.

16. The process of claim 12 wherein said aqueous electrolyte is an aqueous hydrochloric acid solution.

17. The process of claim 12 wherein said solvent is selected from the group consisting of methanol, ethanol, butanol, allyl alcohol, benzyl alcohol, glycol, water, carbon disulfide-phosphorus, ethyl ether, anhydrous ammonia, and mixtures thereof.

18. The process of claim 12 wherein said solvent is ethanol.

19. The process of claim 12 wherein said solvent is ethyl ether.

20. The process of claim 12 wherein said solvent is anhydrous ammonia.

21. The process of claim 12 wherein the concentration of said elemental phosphorus to said solvent is between about 0.0001 percent and about the saturation concentration.

22. The process of claim 12 wherein said catholyte is maintained free from contact with said anode.

23. The process for the production of phosphine in an electrolytic cell comprised of a lead cathode, a catholyte, an aqueous phosphoric acid anolyte and a lead oxide anode, which comprises dissolving elemental phosphorus in ethanol, admixing the resulting ethanol solution with an aqueous phosphoric acid solution, whereby a colloidal dispersion of elemental phosphorus is obtained, contacting the resulting colloid-containing solution as said catholyte with said cathode, and passing an electric current between said cathode and said anode through. said catholyte and said anolyte, whereby a phosphine-containing gas is produced at the cathode.

References Cited in the file of this patent UNITED STATES PATENTS 1,375,819 Blumenberg Apr. 26, 1921 2,408,036 Boetger et al Sept. 24, 1946 2,872,405 Miller et al. Feb. 3, 1959 FOREIGN PATENTS 1,130,548 France Oct. 1, 1956 OTHER REFERENCES Ephraim: Inorganic Chemistry, 1948, pages 134-138.

Journal of the Electrochemical Society, January 1957, volume 104, No. 1, pages 21-29.

Handbook of Chemistry and Physics, 38th Edition, pages 564-5, by Chemical Rubber Publishing Company. 

1. THE PROCESS FOR THE PRODUCTION OF PHOSPHINE IN AN ELECTROLYTIC CELL COMPRISED OF A CATHODE, A CATHOLYTE, AN ANOLYTE, AND AN ANODE, WHICH COMPRISES DISSOLVING ELEMENTAL PHOSPHORUS INA POLAR SOLVENT, CONTACTING THE RESULTING SOLUTION AS SAID CATHOLYTE WITH SAID CATHODE, AND PASSING AN ELECTRIC CURRENT BETWEEN SAID CATHODE AND SAID ANODE THROUGH SAID CATHOLYTE AND SAID ANOLYTE, WHEREBY A PHOSPHINE-CONTAINING GAS IS PRODUCED AS THE CATHODE. 